1,2

a(n) gives the row length of the irregular triangle A290600.

Table of n, a(n) for n=1..50.

a(n) = number of positive numbers k < A002808(n) with gcd(A002808(n), k) not 1.

a(4) = 2 because A002808(4) = 9, with the two non-coprime positive numbers smaller than 9, namely 3 and 6. See row n = 4 of A290600.

Cf. A002808, A290600.

Sequence in context: A265751 A143050 A214919 * A070163 A083343 A292527

Adjacent sequences: A290596 A290597 A290598 * A290600 A290601 A290602

nonn

Wolfdieter Lang, Aug 30 2017

approved